Mechanisms of reactions of halogenated compounds Part 7. Effects of fluorine and other groups as substituents on nucleophilic aromatic substitution

The effect of fluorine as a substituent group on nucleophilic aromatic substitution is discussed, where a fluorine atom located ortho to the point of substitution may be of variable activating influence, whereas fluorine located para is slightly deactivating and meta is activating. A rationale of these effects is presented and evidence to support polar influences by ortho fluorine is advanced. The influence of CN, CF(3), CF(2)H and CFH(2) is also established by comparison of appropriate measured rate constants and compared with the activation effects of ring nitrogen. (C) 2008 Elsevier B.V. All rights reserved.